AFP/Getty Images(WASHINGTON) -- The United States has concluded that Syrian President Bashar al-Assad's regime has used chemical weapons in the fight against its own people, the White House announced on Thursday.

"Following a deliberative review, our intelligence community assesses that the Assad regime has used chemical weapons, including the nerve agent sarin, on a small scale against the opposition multiple times in the last year," Deputy National Security Advisor for Strategic Communications Ben Rhodes said in a written statement. "The use of chemical weapons violates international norms and crosses clear red lines that have existed within the international community for decades."

While traces of chemical weapons in Syria were detected by the U.S. intelligence community months ago, President Obama and his administration had delayed making a determination on who had used the deadly agents.

The president has said repeatedly that the use of chemical weapons would cross a "red line" and be a "game-changer" that would prompt greater American involvement in the crisis.

"The president has said that the use of chemical weapons would change his calculus, and it has," Rhodes said.

The intelligence community estimates that 100 to 150 people have died from chemical weapons attacks in Syria to date.

Rhodes told reporters on a conference call late Thursday afternoon that the administration has prepared for many contingencies in Syria but that "we are going to make decisions on further actions on our own timeline."

"We have not made any decision to pursue a military operation such as a no-fly zone," he added.

Rhodes said the U.S. will increase "direct support" to Syrian rebels in an effort to make them more effective, but he stopped short of saying whether the White House was planning to arm them.

"I cannot detail for you all of the types of that support for a variety of reasons," Rhodes said. "The president has made a decision, in part because of the assessed use of chemical weapons, to provide additional types of support to the [Supreme Military Council]."

On Friday, however, a U.S. official confirmed to ABC News that the stepped up aid will include small arms.

Lawmakers from both parties have called on the Obama administration to do more regarding Syria.

Sen. John McCain, R-Ariz., who has been vocal on the need for more U.S. action against the Assad regime, praised the finding by the government and pressed Obama to offer "lethal assistance" to rebel forces.

"But providing arms alone is not sufficient," said McCain in a joint statement with Sen. Lindsey Graham, R-S.C. "That alone is not enough to change the military balance of power on the ground against Assad. The president must rally an international coalition to take military actions to degrade Assad's ability to use air power and ballistic missiles and to move and resupply his forces around the battlefield by air. This can be done, as we have said many times, using stand-off weapons such as cruise missiles."

"We cannot afford to delay any longer," the senators added. "Assad is on the offensive with every weapon in his arsenal and with the complete support of his foreign allies. We must take more decisive actions now to turn the tide of the conflict in Syria."

"Every bone in my body knows that simply providing weapons will not change the battlefield equation and we must change the battlefield equation," McCain later added on the Senate floor. "Otherwise, you are going to see a regional conflict the consequences of which we will be paying for a long, long time."

Sen. Saxby Chambliss, R-Ga., who sits on the Senate Intelligence Committee, said Thursday night he would support an American military operation against Syria.

"I have said for the last several weeks that doing nothing, [to] continue to do nothing, is not an option," said Chambliss. "We know now that almost 100,000 or maybe an excess of 100,000 people have been killed inside Syria -- and the United States has sat by and watched that happen. We now know that the president said a red line was the use of chemical weapons. We know now that chemical weapons have been used for almost a year by the Syrian regime. We've done nothing. I think it's time that we act in a very serious way. If a no fly zone is what they've decided to do, I am sure our military is taking the right preparations for carrying out a successful operation. And I will support that."

The Office of the United Nations High Commissioner for Refugees issued updated casualty estimates on Thursday that identified 92,901 documented cases of individuals killed in Syria between March 2011 and the end of April 2013 and more than 5,000 killings documented every month since last July.

The UNHCR reported that there have been 27,000 new killings in Syria in 2013 and more than 6,000 children have been killed during the war.